With the increasing power of consumer electronics, the capacity of a battery pack applied in such consumer electronics is also increasing. Typically, a battery pack with a relatively large capacity may include several batteries. Thus, different batteries should be balanced during the operation process, in order to improve the utilization factor of the batteries. In addition, some of the batteries should be protected against being over-charged or over-discharged, as it may shorten the battery lifetime. As shown in the conventional scheme of FIG. 1, the batteries are balanced by using capacitors and related switch loops coupled between every two adjacent batteries. However, such approaches can only exchange energy between adjacent batteries, and are unable to freely exchange energy between all of the batteries. Moreover, a large number of capacitors are needed in this type of arrangement, so the efficiency may be relatively low as the charge transfer efficiency equals to a ratio of a voltage of one battery with a lower charge to a voltage of another battery with a higher charge.